This invention relates to motor vehicles powered by heat engines, such as trucks that are powered by internal combustion engines.
A thermodynamic system in which mechanical energy is extracted from heat energy must reject some heat as waste heat. Heat transfer occurs through one of three phenomena: conduction, convection, and radiation. In the case of a heat engine, such as an internal combustion engine of a motor vehicle, that converts heat energy of combustion into mechanical energy for powering the vehicle, the amount of heat that needs to be rejected typically requires that the engine have its own cooling system, typically air-cooled or liquid-cooled. Air-cooling, where heat transfer occurs directly from the engine to ambient air, may be adequate for certain small engines, but motor vehicles that are powered by large engines typically require a liquid cooling system for the engine.
As liquid coolant is circulated through coolant passages in the engine block and heads that form the engine combustion chambers, some of the heat of internal combustion transfers by conduction to the circulating liquid. Coolant is circulated in a loop that runs from the engine to a heat exchanger, i.e. a radiator, and back to the engine. The radiator serves to reject heat from the circulating coolant by conductive transfer to ambient air that flows through the radiator. The flow rate of ambient air through the radiator affects the heat transfer rate.
Placement of a radiator in a vehicle may seek to take advantage of ram air for forcing the flow of ambient air through the radiator. Under certain conditions, the ram air flow may be sufficient for adequate heat rejection. Under other conditions, it may not. Consequently, such a motor vehicle may have an engine cooling fan associated with the radiator to force ambient air through the radiator when ram air is inadequate.
Although it was once a common design practice for an engine cooling fan to be driven directly from the engine via a fan belt, various considerations like fuel economy and fan noise have impacted both cooling fan design and the way in which the cooling fan is driven. Whenever ram air flow is adequate for engine cooling needs, operation of an engine cooling fan is wasteful of energy. Hence, various forms of electric control for engine cooling fans have emerged, a basic purpose being to disconnect the fan from the engine when it is not needed, such as when ram air is sufficient to satisfy engine cooling needs.
An electro-mechanical device, such as a clutch, is one type of interface between an engine and its cooling fan. An electric signal selectively engages and disengages the clutch to selectively connect and disconnect the cooling fan to and from the engine. One way of developing the electric signal is via suitable algorithms in the processor of an electric engine control system.
Motor vehicles fall within the purview of certain government regulations. Fuel economy, tail-pipe emissions, and noise are examples such regulations. As an element for achieving compliance with applicable fuel economy regulations, it is desirable for certain engines to selectively connect and disconnect an engine cooling fan to and from the engine according to engine cooling needs. This type of fan control is sometimes called an xe2x80x9con-offxe2x80x9d control.
Because operation of an engine cooling fan can contribute to the noise generated by a motor vehicle, it may be important to control fan noise as an element of compliance with applicable noise regulations. At the same time, it is important that such control not impede the attainment of adequate engine cooling when the fan needs to be used to achieve such cooling.
The present invention is directed toward a novel engine cooling fan control that takes into account both compliance with applicable government regulations and engine cooling needs so as to assure that both considerations are properly addressed in a new motor vehicle covered by such regulations. The invention has an advantage of being capable of implementation in an existing engine control system using existing hardware. This is because the inventive principles can be implemented as part of the cooling fan control strategy in a processor of the engine control system.
Accordingly, one generic aspect of the present invention relates to an engine cooling fan control in a motor vehicle powered by a heat engine having an engine cooling fan coupled to the engine through an interface that is operable to selectively place the cooling fan in driven and non-driven relationship with the engine. With the engine running, an engine control system controls the interface to place the cooling fan selectively in driven relationship with the engine for forcing ambient air to contribute to engine cooling and in non-driven relationship with the engine to discontinue forcing ambient air to contribute to engine cooling. The engine cooling fan control comprises a strategy in the control system for indicating when engine speed exceeds a reference engine speed, for indicating when vehicle speed exceeds a reference vehicle speed, and for indicating when rate of change of engine speed exceeds a selected rate of change of engine speed. The strategy causes the interface to place the cooling fan in non-driven relationship with the engine when vehicle speed exceeding the reference vehicle speed is indicated coincident with indication of either engine speed exceeding the reference engine speed or rate of change of engine speed exceeding the selected rate of change of engine speed.
Another generic aspect relates to a method of engine cooling fan control in a motor vehicle powered by a heat engine having a cooling fan that is operated selectively by the engine to force ambient air to contribute to engine cooling when placed in driven relationship with the engine and not to force ambient air to contribute to engine cooling when placed in non-driven relationship with the engine. The method comprises processing engine speed data, reference engine speed data, and selected rate of change of engine speed data to indicate engine speed exceeding a reference engine speed and to indicate rate of change of engine speed exceeding a selected rate of change of engine speed. Vehicle speed data and reference vehicle speed data are processed to indicate vehicle speed exceeding a reference vehicle speed. The cooling fan is placed in non-driven relationship with the engine when vehicle speed exceeding the reference vehicle speed is indicated coincident with indication of either engine speed exceeding the reference engine speed or rate of change of engine speed exceeding the selected rate of change of engine speed.
Still another generic aspect relates to a motor vehicle comprising a heat engine that powers the vehicle and comprises an engine cooling fan coupled to the engine through an interface that is operable to selectively place the cooling fan in driven and non-driven relationship with the engine. With the engine running, a control system controls the interface to place the cooling fan selectively in driven relationship with the engine for forcing ambient air to contribute to engine cooling and in non-driven relationship with the engine to discontinue forcing ambient air to contribute to engine cooling. The control system processes certain data for indicating when engine speed exceeds a reference engine speed, for indicating when vehicle speed exceeds a reference vehicle speed, and for indicating when rate of change of engine speed exceeds a selected rate of change of engine speed, and causes the interface to place the cooling fan in non-driven relationship with the engine when the processing of the data discloses vehicle speed exceeding the reference vehicle speed coincident with the processing of the data disclosing either engine speed exceeding the reference engine speed or rate of change of engine speed exceeding the selected rate of change of engine speed.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.